A container can be considered as a box made of steel. Instead of steel other strong enough materials could be also used. There are five common standard lengths for containers: 20 ft (6.1 m), 40 ft (12.2 m), 45 ft (13.7 m), 48 ft (14.6 m) and 53 ft (16.2 m). The container capacity is measured in twenty-foot equivalent units (TEU). A twenty-foot equivalent unit is a measure of containerized cargo capacity equal to one standard 20 ft (length)×8 ft (width)×8 ft 6 in (height) container. In metric units this is 6.10m (length)×2.44 m (width)×2.59 m (height). Thus, the capacity of one TEU is approximately 39 m3. Most containers today are of the 40-ft and thus also known as 2 TEU.
“Containerization” is a term related to logistics that changed freight handling in the 20th century. A basic idea of the containerization is that a mode of transportation of cargo must be easily transformed into another.
For example, if a container is placed in a train, the container can be moved from the train to a ship and from the ship to a truck. The container is usually lifted up many times from the ground and moved to another place during its transportation. For example, forklifts, portainer cranes, and other types of devices move the container. These devices may also place the container in a pile of containers to wait the next step in the transportation. The above-mentioned length standards and other standards specified by ISO (international organization for standardization) simplify and speed up the handling of the container and the logistics related it.
Containerization is widely used in sea transport and in cargo shipping. Today, worldwide approximately 90% of non-bulk cargo is transported by containers. The containers are stacked on transport ships that can carry up to 9,000 TEU and even larger ships are intended to take in use in the future.
In the following we discuss about the prior art related to the invention.
U.S. Pat. No. 6,795,823 describes a system for tracking articles and optimally routing them. The system processes variable factors such as weather, traffic, and available trucks, and generates an optimal route for an article. The system includes global positioning sensors placed in the trucks. In addition to these sensors, the trucks are equipped with modems which send position coordinates obtained from the global positioning sensors via a pager network to the system. This way the system is able to track and route the trucks and the articles stacked in them.
The system of U.S. Pat. No. 6,795,823 operates in land but not at sea. In principle, a container can be continuously tracked in land and at sea when the container includes a satellite locator, satellite transceiver and a satellite antenna, and the position coordinates obtained from the satellite locator are sent through the satellite transceiver and antenna to a tracking system. Typically this requires a clear line of sight from the container to the satellite. In practice, the container may need to be located a number of times during its transportation in such a place that the satellite locator and/or the satellite transceiver and antenna is temporarily out of order due to lack of the line of sight to the satellite.
In a ship, in a harbor, or in other stock area the container may reside in the bottom layer of a huge pile of containers and for that reason it is not possible to connect to the container through its satellite antenna.
Furthermore, a great number of containers are loaded in a ship in cargo holds. The cargo holds are entirely isolated sections of the ship which are made of steel preventing all satellite connections to the containers.
One aspect related to connections is that satellite connections are expensive when comparing them to pager network connections or cellular network connections. This and other aspects are considered in U.S. patent application Ser. No. 10/994,781, published as US 2006/0109106 A1.
U.S. patent application Ser. No. 10/994,781 describes a monitoring system for a container. The system includes a central computer and an onboard device attached to the container. The onboard device includes a satellite modem and one or more sensors for sensing the conditions of the container. If a sensor of the onboard device alerts, the alert is sent through the satellite antenna to the central computer of the system. As an example, the sensor alerts, if someone breaks in into the container.
In one embodiment, the onboard device of U.S. patent application Ser. No. 10/994,781 further includes a short-range wireless communication module and/or a cellular telephone modem. Therefore the onboard device can alternatively send its alert via a short-range wireless network or via a cellular network to the central computer. In addition, the system may include fixed communication devices for creating communications hotspots.
A communication hotspot receives through its short-range wireless communication module an alert sent by the onboard device and transmits the alert to the central computer. The communication hotspot can be used in a ship, in a harbor, or in other area where containers are piled and the radio environment is very challenging.
The communication hotspot solves some of the problems related to the connections to the containers, but not all of them.
One drawback of the prior art is that container monitoring systems are too unreliable in a challenging radio environment. The communication hotspots work poorly when containers are stacked in a large group. In such group it is common that one or more containers cannot reliably communicate with the hotspot or with any network.
The use of different types of communication networks solves some of the problems related to the connections to the containers, but not all of them, because “a connection set-up logic” is missing.
Another drawback of the prior art is that the connection set-up logic for different types of communication networks is not properly specified.